1. Field of the Invention
This invention relates to the field of automatic data collection in remote and harsh environments and more specifically to the field of providing a combined isothermal cavity and spark gap protection assembly for input/output connection terminals for electronic modules used in such data collection.
2. Background Discussion
Automatic data collection in remote and harsh environments presents several fundamental design problems that must be addressed from the outset. This is particularly true if low level measurements (e.g., micro-volt level) are going to be accurately made in locations where only limited power (e.g., one watt) is available. Principal among these problems in regard to the collection of low level measurements is eliminating spurious voltages at the terminal pin connections to the modules. Such spurious voltages can be due to any number of causes but one of the primary ones is temperature gradients across the terminal pin connector panel. At the micro-volt level, even the slightest temperature gradients can create sufficient therminal voltages and spurious signals to render impossible the direct connection of certain sensors such as thermocouple, strain gauge bridge, and low resistance devices. Presently, such data is either simply not collected or only collected where sufficient power is available to use amplifiers. However, even where sufficient power is available, the use of amplifier-per-channel in rugged and harsh environments often adds undesirable costs, weight, and complexity. Further, and perhaps more importantly, it can introduce significant errors in the low level measurements particularly where ambient conditions such as temperature may vary significantly and automatic calibration techniques using microprocessor control cannot be employed in a cost effective manner in amplifier-per channel systems.
In addition to eliminating thermal gradients across the terminal pin connector panel, another problem in the automatic collection of data in remote and harsh environments is protecting the module from high potential voltage surges in the signal lines. Such surges are simply unavoidable in most outdoor environments where they can be generated from a number of sources including lightning. Consequently, it is essential that the circuitry of the modules be protected from such high voltage surges.
With these problems in mind, the present invention was developed. With the present invention, low level measurements on the micro-volt level can be accurately and directly collected in remote and harsh environments using minimum power requirements on the order of one watt. In doing so, the invention presents a simple and compact arrangement for creating an isothermal cavity about the terminal pin connector panel. With this arrangement, spurious voltages due to thermal gradients across the panel have been essentially eliminated and direct measurement of multiplexing low level signals is now possible in the field with laboratory accuracy. Additionally, the present invention has incorporated a unique spark gap protection system into its design while maintaining the overall simplicity and compactness of the system.